Automatic Bypass Valve Setting For Smart Pump

[Ballantine]

I wonder if somebody could advise as to the right pressure setting for a spring loaded bypass valve when used with a Wilo Smart Pump. It seems easy enough with a fixed bypass - simply shut off everything and adjust for the minimum flow rate, which is .25l/sec. With no fixed pressure curves for the pump and no flow indicator, though, I don't understand how to calculate the correct setting in bars.

 

[croydoncorgi]

The bypass setting is NOT related to the pump: it's to do with your boiler's required minimum flowrate. The combination of bypass and smart pump may not do what your boiler needs.

The pump's smart logic probably calculates what actual output pressure it's producing (I assume the Wilo one does this... just struggled with the Wilo website to try to identify which pump you have & its likely performance -and gave up! Is it a Stratos 25/1-8?) If the result is just more than the pressure required to drive your system but still just less than the bypass setting, your boiler will be unhappy! OTOH, if you have a 'real' bypass load such as a heated towel rail on all the time, you probably won't need any other bypass at all - the pump will deal with the problem.

More details of the setup, please.

 

[chrishutt]

The smart pump has to ensure the minimum flow through the boiler required to avoid overheating. The by-pass must be adjusted to ensure that you get the minimum flow, but it's variable resistance will presumably feed back to the smart pump so it might take a while to settle down to a stable flow rate.

What you really need is some sort of flow meter - perhaps temporarily insert a water meter and run the system cold? Otherwise I expect you will have to adjust by trial and error - too low a flow and the boiler overheat cutout will operate. Perhaps Wilo can advise.

 

[Ballantine]

Thanks for both replies, but I should have made it clear that I am aware of what the bypass valve is for, and I am perfectly able to read the correct setting from the curves supplied for a normal pump. It seems to me, though, that a differential bypass valve and the Smart Pump (model 25/6-30 for the record) will constantly be fighting each other to control the flow rate. I did ask Wilo, and was told to set the valve to the maximum output pressure for the pump setting, ie 3bar for the lowest pump setting. They could not explain how this would work, though, and it makes no sense to me, as the pump would change its effort as soon as the valve opened, and so it would go on.

I was hoping someone with professional experience of this kind of pump could either explain how it works, or confirm my belief that smart pumps don't go with differential bypass valves.

 

[croydoncorgi]

Sorry - the only electronic-control pumps I use are Grundfos Alpha and Magna.

No docs for Wilo ?? Smart 25/6-30 that I can find so no information how far 'smartness' goes. Is it just constant-pressure? or what?

 

[Dan Robinson]

Might have to check, but I was under the understanding that smart-pumps were better with fixed by-passes. Two-speed pumps like the Clesius an Coopra were fine with differential by-passes though.

 

[AndyN11]

I have exactly the same query and exactly the same stone walling , have you had this problem resolved?

 

[BigBurner]

I have exactly the same query and exactly the same stone walling , have you had this problem resolved?

You might want to put a plate heat exchanger on the flow & return to the boiler. Have a fixed speed pump on the flow or return of the boiler - the boiler only flow through the plate heat exchanger. On the other side of the plate have the flow and return to the CH and cylinder. On this side have the smart pump and flow switch in front. The flow switch switches the boiler and fixed rate pump in and out.

The advantages are:

1. 
   [*]The plate heat exchanger 100% protects the boiler as it is always at full flow through the boiler
   [*]No sludge from the raditors enters the boiler at all as it is 100% isolated from the harmful system.
   [*]The boiler stays super clean.
   [*]No by-pass valves needed.

Well worth doing.

 

[Agile]

Another example of totally irrelevant nonsence from BB. He seems to be getting worse as he gets older!

We see very few smart pumps but they dont seem to present much of a problem.

The pumps interpret the current taken to indicate the pumping flow resistance.

This question is only a problem in the owners mind. The reality of the practical situation is that there is not any problem.

I would suggest that you turn off all rads except one and then set the auto bypass to just allow a small flow through it.

The scales on bypasses are either arbitrary or in metres head of water. ( Not in Bar ! ).

Tony

 

[BigBurner]

Another example of totally irrelevant nonsence from BB.

I know it is not a thermocouple, but what didn't you understand?

Read this....

This question is only a problem in the owners mind. The reality of the practical situation is that there is not any problem.

So the OP is imaging all this. Amazing. He then goes on.....

I would suggest that you turn off all rads except one and then set the auto bypass to just allow a small flow through it.

He is offering a practical solution, so the OP is not imaging all this after all.

Stick to thermocouple changing please.

 

[Agile]

So the OP is imaging all this. Amazing. He then goes on.....

He is offering a practical solution, so the OP is not imaging all this after all.

Stick to thermocouple changing please.

Imaging is the formation of an image.

It seems that your mental processes are in decline and you can no longer remember words!

I expect that you really would have used the word imagining if only you have been able to remember what the word was!

Dont get too worried, its quite normal for mental processes to decline when you get old.

An elderly doctor I went to yesterday had a good brain but his hands shook and particularly when he was stressed until I had fixed his equally elderly boiler ( a Servowarm ! ).

Tony

 

[Norcon]

Agile wrote

Another example of totally irrelevant nonsence from BB

Why is what he wrote irrelevant nonsense?
And I think you should get your own spelling correct before judging others!
(Btw the setting range on Danfoss by-pass valves are marked in Bar)

 

[AndyN11]

It seems that the person who raised the original question no longer in the forum so I repeat my problem.
I have a Worcester Bosch 18Ri gas fired boiler installed the design of the boiler is such that it controls the circulating pump and so far all is well but I have a question for which I would be gratefull if you would answer. I have the S plan system all installed to British Gas recommendations it has a bypass with an automatic bypass valve set a 0.35 bar and the pump is a Wilo Smart pump (set at the mid position) operating according to the pump curves between 2.3m and 3.5 m head and this pump automatically adjusts speed to any changes in the system needs/restictions. My concern is that when the boiler stops firing as called by the room thermostat, the CH and hot water motorized valves will close but the boiler will still run the circulating pump for another 6 minutes as required but in this situation the pump will slow down automatically because the motorized are closed, will this be enough to force open the automatic bypass valve? or should I have a fixed speed pump?.
The pump delivery is to the 2 motorised valves and the bypass.

 

[deenrbe]

I have been having the same problem with a Worcester 24Ri boiler, Grundfos Alpha2 pump and Danfoss Avdo auto bypass. After talking to Worcester and looking at the data sheets for pump and bypass I have decided that I am replacing the auto bypass with a good old fashioned gate valve.

The reasons?

With a traditional pump, as the trv's or zone valves close, and the flow reduces (or stops) there is an increase in discharge pressure from the pump as it tries to push against the closing valves. This increase is what forces a correctly set bypass valve off it's seat thus maintaining flow through the boiler.

With an intelligent pump the pump senses the drop in flow as trvs close and slows itself down, LOWERING the discharge pressure to save energy. This prevents the rise in pressure that should have opened the auto bypass, preventing it from fulfilling it's purpose (BYE BYE boiler!).

In fact the Grundfos Alpha 2, set to factory default, actually has a lower discharge pressure against a closed valve than an open one!!!!

So, IMHO don't use the spring loaded auto bypass with a smart pump.

If you have an Alpha 2 you can always set it to constant speed and keep the auto bypass, but then why spend the money on the pump in the first place?

The Grundfos manual does mention THERMOSTATICALLY controlled bypass valves. These are a completely different beasty and i can find no mention of them anywhere for domestic use.

 

[D_Hailsham]

The Grundfos manual does mention THERMOSTATICALLY controlled bypass valves. These are a completely different beasty and i can find no mention of them anywhere for domestic use.

I think it is a typo and Grundfos mean Automatic bypass valve. There is no mention of Thermostatic bypass valves in the Grundfos Installers Handbook.